The present invention relates generally to disc type attrition mills and more particularly to a disc type refiner having a refiner casing and an attached feed screw housing.
Disc refiners of this type are widely used in paper pulp processing and are characterized by a rotor supporting a concentric disc. A set of refining plates is mounted on one or both axial faces of the disc. The refining plates are available in a variety of patterns and plate faces typically are in a ribbed or toothed pattern. A stationary set of refiner plates is disposed in juxtaposed relation to the plates of the disc on the rotor, and the material to be refined is introduced near the rotor axis between the opposing plate surfaces. The relative rotation of the plates centrifugally advances the material radially across the plate surfaces and the relatively close spacing of the plates breaks down the material fibers. In a common embodiment of such disc type refiner, a screw or ribbon feeder is associated with the rotor, and extends in a housing which is rigidly connected to the refiner casing. Typically, another screw arrangement is connected to the feed screw housing to supply raw material from a storage bin.
The spacing between the rotating, or rotating and stationary plates, is typically in the range of 0.04 to 0.10 inches during the refining operation. A recurring problem with refiner of this type, is that external loads developed by thermal expansion of connecting pieces and pressure forces developed by flexible expansion joints associated with the housing and casing, have not been well isolated from the refiner casing. If such external loads on the feed screw housing are not isolated from the refiner casing, they can adversely effect the operation of the refiner by causing distortion of the refining surfaces and causing the refiner to go out of tram, i.e., base parallelism of the refining plates.
Conventional techniques for accommodating these external loads do not fully compensate for all directions of thermal expansion and externally applied piping loads. A typical prior art arrangement is shown in U.S. Pat. No. 3,847,359 (Holmes et al), "Disc Type Refiner With Automatic Plate Spacing Control", which discloses a rotor mounted in a bearing set, which in turn is mounted in a member that is slidably disposed within the housing to permit axial displacement of the bearing without changing the position of the rotor with respect to the base of the refiner. Although this arrangement can accommodate horizontal stresses, it can not readily accommodate vertical stresses.
U.S. Pat. No. 4,688,732 (Jackson), "Refiner With Improved Bearing Retainer Construction", also disclosed a bearing assembly which can accommodate displacement between a rotor and its enclosure, but, as with the previously mentioned patent, only in the axial, i.e., horizontal, direction.